Acquisition of a SPEX Instruments CM/IM system for fluorescent determination of intracellular ion concentration and pH in single cells and multicellular systems is proposed. In recent years, development of several fluorophores such as Quin-2, Fura-2 and Indo-1 which bind to Ca2+ and fluoresce has led to the ability to make quite precise measurements of intracellular Ca from multicellular suspensions. Recent developments in digital imaging have broadened these capabilities to the point were it is now possible to resolve intracellular ion concentrations in single cells both spatially and temporally. The ability to measure intracellular divalent cation concentration spectrofluorometrically would be extremely valuable for several ongoing research projects associated with neurosecretion, metabolic activation and muscle contractility. In particular, this would allow precise determination of target sites of action of certain therapeutic agents such as antibiotics and cardiac glycosides and toxic agents such as dieldrin and methylmercury. In addition, through acquisition of this system more generally-related problems in cell biology such as the coupling of growth factor regulation and secretion to phasic changes in intracellular Ca will be explored.